Selective delivery of insulin into the brain: Intraolfactory absorption

The distribution of insulin between blood and brain was investigated in mice. The drug was administered subcutaneously and by instilling the drug to the olfactory region of the nasal cavity. The concentrations of insulin in the biological samples were measured by a gamma-counter. A significantly higher concentration of insulin was measured in the brain, following intraolfactory administration compared to subcutaneous injection. The absorption was also found to be very rapid. Ten minutes after the administration the concentration in the brain had reached 193 counts/min per g (equivalent to 37 mu U insulin/g tissue), which was 487% higher than achieved after subcutaneous injection. The majority (>99%) of the CNS drug development programmes are devoted solely to CNS drug discovery and less than 1% are devoted to drug delivery. The results suggest that it may be possible to achieve absorption directly into the brain, by-passing the blood-brain barrier. The olfactory region may be the key for this absorption.